如果你正在使用pytest，你可以使用pytest.raise (Exception):

例子:

def test_div_zero():
    with pytest.raises(ZeroDivisionError):
        1/0

结果是:

$ py.test
================= test session starts =================
platform linux2 -- Python 2.6.6 -- py-1.4.20 -- pytest-2.5.2 -- /usr/bin/python
collected 1 items

tests/test_div_zero.py:6: test_div_zero PASSED

或者你可以构建自己的上下文管理器来检查异常是否被引发。

import contextlib

@contextlib.contextmanager
def raises(exception):
    try:
        yield
    except exception as e:
        assert True
    else:
        assert False

然后你可以像这样使用加薪:

with raises(Exception):
    print "Hola"  # Calls assert False

with raises(Exception):
    raise Exception  # Calls assert True

如果你正在使用Python 3，为了断言异常及其消息，你可以在上下文管理器中使用assertRaises，并将消息作为msg关键字参数传递，如下所示:

import unittest

def your_function():
    raise RuntimeError('your exception message')

class YourTestCase(unittest.TestCase):
    def test(self):
        with self.assertRaises(RuntimeError, msg='your exception message'):
            your_function()


if __name__ == '__main__':
    unittest.main()

如果在这个类中将stock_id设置为Integer将抛出错误，则将引发TypeError，如果发生这种情况，则测试将通过，否则将失败

def set_string(prop, value):
   if not isinstance(value, str):
      raise TypeError("i told you i take strings only ")
   return value

class BuyVolume(ndb.Model):
    stock_id = ndb.StringProperty(validator=set_string)

from pytest import raises
buy_volume_instance: BuyVolume = BuyVolume()
with raises(TypeError):
  buy_volume_instance.stock_id = 25

这里有很多答案。该代码展示了如何创建Exception，如何在方法中使用该异常，以及如何在单元测试中验证所引发的正确异常。

import unittest

class DeviceException(Exception):
    def __init__(self, msg, code):
        self.msg = msg
        self.code = code
    def __str__(self):
        return repr("Error {}: {}".format(self.code, self.msg))

class MyDevice(object):
    def __init__(self):
        self.name = 'DefaultName'

    def setParameter(self, param, value):
        if isinstance(value, str):
            setattr(self, param , value)
        else:
            raise DeviceException('Incorrect type of argument passed. Name expects a string', 100001)

    def getParameter(self, param):
        return getattr(self, param)

class TestMyDevice(unittest.TestCase):

    def setUp(self):
        self.dev1 = MyDevice()

    def tearDown(self):
        del self.dev1

    def test_name(self):
        """ Test for valid input for name parameter """

        self.dev1.setParameter('name', 'MyDevice')
        name = self.dev1.getParameter('name')
        self.assertEqual(name, 'MyDevice')

    def test_invalid_name(self):
        """ Test to check if error is raised if invalid type of input is provided """

        self.assertRaises(DeviceException, self.dev1.setParameter, 'name', 1234)

    def test_exception_message(self):
        """ Test to check if correct exception message and code is raised when incorrect value is passed """

        with self.assertRaises(DeviceException) as cm:
            self.dev1.setParameter('name', 1234)
        self.assertEqual(cm.exception.msg, 'Incorrect type of argument passed. Name expects a string', 'mismatch in expected error message')
        self.assertEqual(cm.exception.code, 100001, 'mismatch in expected error code')


if __name__ == '__main__':
    unittest.main()

从http://www.lengrand.fr/2011/12/pythonunittest-assertraises-raises-error/:

首先，这里是dum_function.py文件中对应的(仍然是dum:p)函数:

def square_value(a):
   """
   Returns the square value of a.
   """
   try:
       out = a*a
   except TypeError:
       raise TypeError("Input should be a string:")

   return out

下面是要执行的测试(只插入这个测试):

import dum_function as df # Import function module
import unittest
class Test(unittest.TestCase):
   """
      The class inherits from unittest
      """
   def setUp(self):
       """
       This method is called before each test
       """
       self.false_int = "A"

   def tearDown(self):
       """
       This method is called after each test
       """
       pass
      #---
         ## TESTS
   def test_square_value(self):
       # assertRaises(excClass, callableObj) prototype
       self.assertRaises(TypeError, df.square_value(self.false_int))

   if __name__ == "__main__":
       unittest.main()

现在我们准备好测试我们的函数了!下面是运行测试时发生的情况:

======================================================================
ERROR: test_square_value (__main__.Test)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_dum_function.py", line 22, in test_square_value
    self.assertRaises(TypeError, df.square_value(self.false_int))
  File "/home/jlengrand/Desktop/function.py", line 8, in square_value
    raise TypeError("Input should be a string:")
TypeError: Input should be a string:

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)

TypeError实际上被引发，并生成一个测试失败。问题是，这正是我们想要的行为:s。

要避免此错误，只需在测试调用中使用lambda运行函数:

self.assertRaises(TypeError, lambda: df.square_value(self.false_int))

最终输出:

----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

完美!

．.． 对我来说也是完美的!!

非常感谢，Julien Lengrand-Lambert先生。

这个测试断言实际上返回一个假阳性。这是因为'assertRaises'中的lambda是引发类型错误的单元，而不是被测试的函数。

使用unittest进行单元测试将是首选，但如果您想快速修复，我们可以捕获异常，将其赋值给一个变量，并查看该变量是否是该异常类的实例。

假设我们的坏函数抛出一个ValueError。

    try:
      bad_function()
    except ValueError as e:
      assert isinstance(e, ValueError)